Communication system



Jan. 6, 1942.

Filed April '7, 1941 rizvv /ewch- Patented Jan, 6, 1942 UNITED STAT Es PATENT- OFFICE,-

conr'rnmrcnrron srs'rsn Richard 1!. Campbell, Racine, Wia, assignor to =Webstcr Electric Company, Racine, Win, a cornotation of Dclawarc Application April '1, 1941, Serial No. 387,181

17 Claims. (on. 1-19- 4) The present invention relates to intercommunicating systems and more particularly to intercommunicating systems of the loudspeaking type employing amplifiers.

One well-known type of intercommunicating systemcomprisesa number of stations, usually called central or master stations, each having an operative amplifier at the master station is rendered" operative so that the sub-station may call the master station.

Other objects and advantages of the present invention willbecome apparent from the ensuing description, in the course of which reference is had to the accompanying drawing, the single figure of which represents schematically one embodiment of the invention.

Referring now to the drawing, there is illustrated an intercommunication system of the loudspeaking. type wherein communication is carried on alternately in opposite directions between a plurality of master stations under the control of manually operable communication direction control switches and wherein communireception of calls through the amplifier; and in a third position, the talk position, the connections of the interstation circuit and the loudspeaker to the amplifier are reversed. The communication control switch also controls the supply of "B voltage to the amplifier. In the idle-listen position, the B supply is cut off to render the amplifier inoperative, but in the-other positions,

the B supply is connected to the amplifier to render it operative for use during reception and transmission.

In a system of the type describechit is possible cation may be carried on between a master station and one or more substations under the control of a communication direction control switch at the master statiom t The master stations are indicated by reference characters I, '2 and 3, and the sub-stations by reference characters 4 and. 5. The stations are provided with translating devices capable of being utilized both as microphones and 1oudspeakers, such as loudspeakers H to IE, inclusive, which may be of the well-known permanent magnet type. The master stations I, 2 and 3 for one station to eavesdropf on another by 7 operating the communication control switch to its listen position and-by operating a selector switch to select another station. When this is done, the loudspeaker at the one station is con nected to the input and the loudspeaker at the other station to the output of the amplifier.

One of the objects of this invention is to provide a new and improved communicating system wherein eavesdropping is prevented and wherein one station can listen to another only when switch means at the latter are operated.

Another object of this invention is the provi-" sion of a new and improved system comprising one or more master stations and one or more sub-stations (stations, provided with a loudspeaker adapted to" be used both as a microphone and receiver but having no amplifier), wherein the master stations are prevented from eavesdropping on each other or upon the sub-stations.

A further object of the invention is to provide a new and improved communication system wherein the master station may be conditioned for reception of calls from sub-stations and the latter are provided with control means so connected in circuit with the amplifier that upon are provided with amplifiers l6, l1 and I8, come munication direction and power control switches.

19,20 and 2|, and station selector switches 22, 23 and 24, all respectively. I

The amplifiers may be of any well-known con- 1 struction and from the figure it may be seen that and 30, the former of which is connected directly switch blade SI of the talk-listen switch I! and operation of the control means, a normallyinconductor SI. The second of. the two circuits'is only amplifier It at station I has been illustrated in detaih In brief, the amplifier comprises an input transformer 25 and an output transformer 26 inter-connected by two. stages of amplification. Power is supplied from a suitable source of alternating current through a transformer 21 and in part through a rectifier tube 28." The supply of rectified current the l3'suppiy) is' v directed to the amplifier through conductors 29 to a common conductor 3| of the amplifier which is grounded preferably through the amplifier chassis, and the latter of which is adapted to be connected to the amplifier tubes through either of two circuits. The first circuit is complated when the communication control switch is operated to its lowermost or talk position, at which time the circuit extends from conductor 30 through conductor 32 and-the. uppermost three-position switch.

up and idle position), the loudspeaker II is con-- completed when the switch blade 33 of the communication control switch is in its middle or listen position, at which time the circuit is completed through the conductor 32, the switch blade 33, a conductor 35, a switch blade 36, operable by a solenoid 31 in a manner to be described in greater detail hereinafter, and conductor 38.

It may be mentioned here, however, that the solenoid 31 is energizable to close switch 36 when the communication control switch i9 is in its listen position and switch means are operated at a selected master or sub-station, so that in the listen position of the communication control switch, the supply of B-voltage to the amplifier is under the conjoint control of an operator at station I and an operator at a selected station.

This conjoint control prevents the undesired eavesdropping referred to heretofore.

The amplifier is conditioned to be ready for instantaneous use whenever the "3 supply circuit is completed by reason of the fact that'the cathode heaters 39 are continuously supplied with heating current from a' secondary winding 40 of the transformer 21.

The communication direction and power control switch I9 is a manually operable multi-pole In a first position (the nected directly to a communication circuit comprising conductors 4| and 42 for the reception of calls from other stations provided with amplifiers, that is, from other master stations. In a second position (the intermediate and listening.

position, as well as a position wherein calls may be received from sub-stations the loudspeaker is connected to the output and the communication circuit to the input of the amplifier. In a third position (the down and talk position, from which the switch is biased by aspring 43 into its intermediate position upon release), the loudspeaker is connected to the input and the communication circuit to the output of the amplifier.

The connection of the loudspeaker to the com munication circuit in the idle position of the communication direction control switch is as follows: from conductor 4| through switch blades 44 and 45 and from conductor 42 through switch blades 46 and 41. that in the idle position of blade 33 is in circuit opening position.

The connection of the loudspeaker to the output and the communication circuit to the input of the amplifier in the intermediate position of thecommunication direction control switch is effected in the following manner: The loudspeak- V er H is connected to the output of the amplifier through switch blade 45 and conductor 48 and through switch blade 41 and conductor 49, the two conductors leading to the terminals of'the secondary winding of the output transformer 26. Conductors 4| and 42 of the communication circuit are connected to the terminals of the primary of the input transformer 25 through switch blade 44 and conductor 56 and through switch blade 46 and conductor 5|.

The connection of the loudspeaker to the input and of the communication circuit to the output of the amplifier in the third position of the communication direction control switch is effected in the following manner: The loudspeaker is connected to the input through switch blade 45 and conductor :50 and through switch blade 41 and conductor 5|. The communication circuit is connected to the output of the amplifier through In passing, it may be noted' the switch, the 3" Lsupply to the amplifier is disconnected as switch ductor 30, and a resistor 54 connected to one terminal of the solenoid, the other terminal of which is grounded. The solenoid is shunted by a current smoothing condenser 55. ously referred to grounding circuit includes a conductor 56 connected to the ungrounded end of the solenoid, a pair of resistors 51 and 58, between which conductor 56 is connected, the communication circuit conductors 4| and 42, switch blades 44 and 46, conductors 59 and 60, the series connected resistors 6| and 62, and the normally closed grounding switch 63 of the push button type connecting to ground the point between resistor -6| and 62. The two pairs of.

resistors 56,, 56, 6| and 62 are all of equal value so as to provide a balanced circuit. This balanced circuit prevents cross talk and undesirable hum that would otherwise result from uneven voltage (the voltage fromthe rectifier used in operating the solenoid) drops in the communication circuit. i E

The selector switch 22 at station I includes a number of switches, as, for instance, the two indicated, by reference character 64, which are termed the station No. 1 switches and which are ordinarily maintained in closed position in order that other stations may communicate with station I. Each of the master stations is preferably 1 provided with as manyv pairs of switches as there switch 2| and the switch blades 65 thereof are closed in order to connect station 2 to the system for reception of calls from other stations. The selector switch 24 at station 3 has not been illustrated in full, but it comprises the switches 66 which are normally'closed to connect station 3 for reception of calls from other stations.

The control circuit at station 2 differs somewhat from that at station I, but it is arranged to perform the same functions as that at station I. The communication circuit conductors at station 2 are indicated'by reference characters 10 and 1|.

. Connected across these in series are resistors 12 and 13, corresponding tothe resistors 51 and 58 at station I. connected through conductor 14 to one terminal of a solenoid 15, the other terminal of which is grounded. The solenoid is shunted by condenser 16 and supplied with energizing current from the 3" supply through resistor 11 and conductor 16. The solenoid controls a switch 16 adapted to interconnect conductors 36 and 6|.

In the idle position of the communication direction control switch, the solenoid 15 is groundedthrough switch blade 62 forming part of thecommunication control switch 20, conductor 83. and a normally closed push button switch 86. The described construction eliminates the second pair'of resistors 6| and 62 found at station I.

The communication control switch 20 includes,

in addition to the switch blade 62, switch blades The previ- The junction of the resistors is 2,269,144 81, 88,89, 90, and 9|, which correspond, respec tively, to switch blades 33, 45, 44, 41, and 46 of the communication'direction control switch I9 at station I. These switch blades are arranged in circuit and perform the same functions as the switch blades of the communication'control switch at station I, so that further description thereof is deemed'to be unnecessary.

The apparatus at station 3 corresponds iden-L tically with that at station I. In brief, the communication circuit comprises conductors 9| and 92, across which are connected'in series the resistors 93 and 94. The junction of the resistors is connected by conductor 95 to a solenoid 95 which is shunted by a condenser 91. The solenoid is supplied with energy from the B sup-.

ply through resistor 98 andconductor 93. The solenoid controls a switch I adapted'to close a circuit between conductors IOI and I02. The communication control .switch includes switch blades I03, I04, I05, I05, and I01, corresponding to switch blades 33, 45, 44, 41, and '45, respectively, of the switch I9 at station I.- In the listen position of the communication control switch, the solenoid 98 is grounded through a circuit'in eluding a second pair of resistors I08, I09 and a normally closed push button switch'I I0.

Station-4 is connected to a pair of conductors I II and H2, and these in turn are connected to interstation conductors individual to station 4. A pair of resistors H3 and H4 are connected in series across conductors III and H2, and the junction of the resistors is connected to ground through a normally closed push button switch The apparatus at station 5 corresponds to that at station 4 except for a station selector switch ground through the interstation circuit and th switch blade 82 and push button switch 86 at .it to itsintermediate or-listen position, and it is also necessary for the operator at station 2 to open the push button switch 85, thereby to open the grounding circuit for solenoid 31. When this is done, the solenoid 31 is energized from the source oi B voltageat. station I, and upon energization, it closes switch 36, thereby to complete the B supply circuit through this switch and through theswitch blade 33 in its intermediate position. Inasmuch as the communication control switch in its listen position connects loudspeaker at station I to the output of the amplifier and the interstation circuit to the in-' put of the amplifier, the operator at station 2 can talk to the operator at station I.

In the event the operator at station 2 desires to call the operator at station I, the same procedure is followed, with the operator at station 2 performing those functions previously per- H5, shown connecting the station to a pair of intel'station conductors III-individual thereto. The selector switch is connected to conductors I I8 and I I9 bridged by a pair of series connected resistors I20 and 'I2I. The junction of the resistors is connected to ground through a normally closed push button switch I22.

In the operation of the system described above,

a it is contemplated that each ofthe amplifiers will normally be supplied with power from a suitable alternating current source through the transformers; and that the communication direction control switches at the various stations will be in their, indicated or i'dle positions, at which time the solenoids at the respective stations will be grounded through circuits including the normally closed push button switches thereat. The station selector switches individual to the respective stations are closed so as to condition the stations fonreception of calls from other stations.

It is assumed now that the operator at station I desires to call the operator at station 2. To, do

this, the operator at station I first closes the second pair of station selector switches thereat to interconnect conductors" and," with conformed by theoperator at station I, and the operator at station I performing the functions previously performed by the operator at station 2, as described above. A

One of the advantages of the foregoing arrangement is that the operator at station I, when communicating with station 2, is unable tolisten to another station, such, for instance, as station 4, by closing the selector switches for connecting that station to station I; ln the event that an attempt is made to do this, the solenoid 31 at station I is grounded through the normally closed push button switch at station 4, and, consequently, the amplifier "3 'supply is broken by the switch 35, thereby rendering it impossible for the operator at station I-to listen to any station, be it station 4 or one of the master stations, such, for instance, asstation 3. This prevents eavesdropping and listening to other stations, except when the grounding switches at these other stations are open.

In the event station I desires to call station 4, the selector switch for the latter station is closed, and the communication .control switchv IQoperated to its talk position. This permits transmission from station I to station 4. Transmission in the reverse directionis possible when the communication control switch is released to 1 switch I I a at station 41s opened.

ductors 4| and 42, respectively, through switch at station 2. This is followed by operation of the communication direction control switch IO' to its lowermost or talk position. Amplifier I5 is rendered operative as the B supply circuit is completed through conductor 32, switch blade 33, and conductor 34. The grounding circuit for solenoid 31 is broken at station I by'reason of the movement 0! switch blades 45 and 41, thereby to disconnect resistors 5| and 52 and ground switch 83 from the solenoid. The solenoid, however, remainsdeenergized as it is connected to its intermediate position and the grounding The control switches at the master stations may be conditioned also forv the reception of calls from sub-stations. This conditioning is effected by leaving the communication control switches. for instance, control switch I9 at station I, in its intermediate position. At that time, the loudspeaker II at station I is connected to the output of the amplifier and the interstation circuit connected to the input. In the event station I is conditioned for reception of calls from station 4, thenthe amplifier at station I is inoperative as the, solenoid 31 would be grounded through push button switch H5. However, the amplifier is rendered operative whenever station 4 opens the grounding switch H5 to initiate acall. After a call has been received by station I, communication may be carried on in opposite directions in the manner described above.

.Yri the,,event station -I is conditioned for reception of calls from stations, such as station 5, provided with selector switches, then the am-' plifier is normally operative as the solenoid 31 is ungrounded. However, when station 5 selects station I, the amplifier is rendered inoperative until grounding switch in at station 5 is opened. Qnce opened, the amplifier is rendered operative in the same manner as though a call were originated from station 4.

In case the communication control switch of' the master station, such as station I, is left in the intermediate or listen position, other master stations may call station I simply by closing the proper station selector switch and opening the grounding switch, such, 'for instance, as switch 86 at station 2 or switch H0 at station 3. The operation in this event is the same as though a call were originated from one of the sub-stations.

While only a few stations have been shown in the embodiment of the invention illustrated and described, it should be understood that the number may be varied as desired, and although the L invention has been disclosed with the specific details of a preferred embodiment, it should be understood that such details are not intended to be limitative of the invention except in so far as set forth in the accompanying claims,

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. In a multiple station intercommunicating system, the combination including, an amplifier sure of said first mentioned switch means and rendering operative the amplifier at a station at which the control switch is in said predetermined position.

2. In a multiple station intercommunicating system of a type wherein a pair of stations are adapted to be connected for two-way communication over a single circuit, the combination including, an amplifier at one of said stations, combined communication'direction and amplifier energization controlling switch means and circuits controlled thereby at said station for connecting said station for reception through said amplifier and for partly completing an energizing circuit' for said amplifier, and means including a switch at another station for completing said energizing circuit.

3. In a multiple station intercommunicating system of a type wherein a pair of stations are adapted to be connected for two-way communication over a single circuit, the combination instation for connecting saidstation for reception through said amplifier and for partly completing the B supply circuit for said amplifier, and means including a switch at another station for completing said B supply circuit.

4. In a multiple station intercommunicating system of a type wherein a pair of stations are adapted to be connected for two-way communication over a single circuit, the combination including, an amplifier at one of said stations, switch means and circuits controlled thereby at said station for connecting said station for reception through said amplifier and for partly completing an energizing circuit for said amplifier, and means including a solenoid and a switch controlled thereby operable to complete said energizing circuit, and a normally closed switch grounding said solenoid at another station operable to an open position for completing said energizing circuit.

5. In a multiple station intercommunicating system of a type wherein a pair of stations are adapted to be connected for two-way communication over a two wire interstation circuit, the combination including, loudspeakers utilizable as microphones and receivers at each station, an amplifier at one of said stations, switch means and circuits controlled thereby at said station for connecting the loudspeaker thereat for reception through said amplifier and interstation circuit and for partly completing an energizing circuit for said amplifier, and means for completing said energizing circuit from another station, said last mentioned means including a pair of resistors connected in series across said interstation circuit at each station, a solenoid connected to a source of power and a point between the pair of' resistors at said one station, a switch controlled thereby and operable upon energization of said solenoid to complete said amplifier energizing circuit, and a normally closed grounding switch connected between the pair of resistors at said other station.

6. In a multiple station intercommunicating system, the combination including, an amplifier at each station, means including a combined amplifier power and communication direction control switch at each station operable to a predetermined position for conditioning the station for reception through the amplifier and partly completing a circuit for rendering the amplifier operative, a solenoid and a switch controlled thereby operable upon energization of the solenoid to complete said circuit, and means including other switch means at each station grounding said solenoid and operable to remove the ground and thereby energize said solenoid and render operative the amplifier at a station at which the first inentioned switch is in said predetermined posiion.

-'7. In an intercommunicating system of the loudspeakng type, comprising a number of statrons each having an amplifier with input and output connections, a loudspeaker utilizable both as a receiver and a microphone, station selector switches for connecting the station to interstation communication circuits and a communication direction and power control switch operable in one position to connect the loudspeaker to an interstation circuit through a station selector switch for reception of calls from other stations in a second position to connect the loudspeaker to the output and an interstation circuit to the input of the amplifier, and in a third position to reverse the connections of the loudspeaker and interstation circuit to the amplifier, the combination including, circuits controlled by each control switch for rendering the amplifier associated therewith inoperative in said first position, for

conditioning for completion a circuit to render the amplifier operative in said second position,

and for rendering operative the amplifier in said third position, a solenoid normally connected to a source of power at each station, a switch controlled thereby for completing the amplifier energizing circuit when the control switch is in said secondposition,and a circuit including a normally closed switch for grounding the solenoid through a portion of an interstaticn circuit when the communication control switch isin said first position, whereby stations with their control switches in their first positions may be called by other stav tions upon operation of the communication control switches at the latter to their third positions and the called stations may answer upon the calling statio'n operating the control switch thereat to its second position and upon opening'the normally closed switch to energize the solenoid and therebycomplete the energizing circuit for the amplifier.

8. A system according to claim 7, comprising,

to which said. solenoid is connected, a pair of resistors connected across an interstation circuit, a connection from said solenoid to the junction of said resistors, a second station, a pair of rethe second station by operating thecommunication control switch thereat to its second position.

12. A unit for use in an intercommunicating system, including in combination, an amplifier, a loudspeaker, a circuit adapted to be connected to other stations, means including a communication control switch operable to a predeter mined position to connect said loudspeaker to the output and said circuitto the input of said amplifier, an energizing circuit for said amplifier p'artly completed by said control switch when in said predetermined position, a switch for comin addition, a number of stations provided with loudspeakers utilizable both as microphones and receivers, and normally closed switches for grounding the interstation circuit, whereby, when the control switches at stations'of the first type are left in their second positions, the substations may transmit messages thereto upon opening of the normally closed switches thereat.

9. In an intercommunicating system, as claimedin claim 7, wherein resistors are conpleting said energizing circuit, and means connected to said circuit and controllable through said circuit forcontrolling said switch.

13. A unit for use in an intercommunicating system IncIuding in combination, an amplifier, a loudspeaker, a circuit adapted to be connected to other stations, means including a communication control switch operable in one position to connect said'loudspeaker to the circuit and in a second position to connect said loudspeaker to the output and said circuit to the input of said amplifier, an energizing circuit for said amplifier partly completed by said control switch nected across the interstation lines at each station and the solenoids are connected to the junction of said resistors'and wherein said junctions are grounded through thenormally closed switches .when the communication switches are in their first positions.

control 10. In amultiple station intercommunicating system, the combination including, a first station, an amplifier thereat, means including a combined amplifier power and communication direction control switchat said station operable to a predetermined position for conditioning the station for reception through the amplifier and partly completing a circuit for rendering the amplifier operative, a normally open switch 'thereat for completing said circuit, means operable to close said switch, a second station, and means including switch means at said second station for causing said last mentioned means to close said switch when the first mentioned switch at the first station is in said predetermined position.

11. In a multiple station intercommunicating system, the combination including, a first station, an amplifier thereat, means including a' combined amplifier power and communication direction control switch at said station operable in one position to condition the station for reception through the amplifier and an interstation circuit and partly to complete an energizing circuit for the amplifier and operable to a secondposition for conditioning the station for when in said second position, a switch for completing said energizing circuit, and means connected to said circuit .and controllable through said circuit for controlling said switch.

14.-A unit for use in an intercommunicating system, including in combination, an amplifier, a

loudspeaker, a circuit adapted to be connected to other stations, means including a communi-- cation control switch operable in one position to connect said loudspeaker to the circuit and in a second position to, connect said loudspeaker to the output and said circuit to the input of said amplifier, an energizing circuit for said amplifier partly completed by said control switch when in said second position, a switch for completing said energizing circuit, a solenoid for controlling said switch, said solenoid being connected to a sourceoi' power, and means including a normally closed switch for grounding said solenoid when said control switch is in'said one position.

v 15. A; unit for use in an intercommun'icating system, including in combination, an amplifier,

aloudspeaker, a circuit adapted to be connected toother stations, means including a communication control switch operable in one position to connect said loudspeaker to said circuit, in a second position to connect said loudspeaker to' the output and said circuit to the input of said amplifier, and ma third position to reverse the connections of said loudspeaker and circuit to said amplifier, an energizing circuit for said amplifier openedby said control switch when in said one position, partly completed by said control switch when in said second position, and completed when in said third position, a normally open switch for completing. said energizing circuit when said control switchis in said second position, and means connected to said circuit and controllable through said circuit for controlling said switch.

16. A unit as claimed in claim 15, wherein said normally open switch is controlled by a solenoid connected to a source of power and to the junction of a pair of resistors connected across said first mentioned circuit, and said junction point is grounded through a normally closed switch in said one position of the communication control switch.

17. In a multiple station intercommuni'cating system, the combination including, a number of stations adapted. to be connected through an interstation circuit and each having an'amplifier,

a loudspeaker utilizable .both as a receiver and a microphone, and a communication control switch normally connecting the loudspeaker to the circuit and operable to connect the loudspeaker to the output and the circuit to the input of said amplifier, and control means at each station for preventing energization of the amplifier at a calling station when the communication control switches thereat are in their said normal positions. a

RICHARD H. CAMPBELL. 

